What are the differences between the “Picatinny” and the “Weaver” systems? The profile of the two systems is virtually identical. Depending on the quality of the machining done by the manufacturer, the two systems should be indistinguishable from the profile. The key difference lies in the placement of the recoil grooves and with width of the grooves. MIL-STD-1913 (Picatinny) grooves are .206” wide and have a center-to-center width of .394”. The placement of these grooves has to be consistent in order for it to be a true “Picatinny” MIL-STD system. Weaver systems have a .180” width of recoil groove and are not necessarily consistent in a center-to-center measurement from one groove to the next. In many instances, a Weaver system has a specific application that it is machined for, so interchangeability is not necessarily an issue. A MIL-STD-1913 system must adhere to the specifications listed above in order for it to be considered MIL-STD, since the military desires uniformity in the recoil grooves to allow for different systems to be mounted on the weapon with no concern for compatibility.

Now, what does this mean to you? Boiled down, it means that accessories designed for a Weaver system will, in most cases, fit on a “Picatinny” system. The reverse, however, is probably not the case. Due to the larger recoil groove, “Picatinny” accessories will not fit a Weaver system. There are, of course, exceptions to every rule, but for a good rule-of-thumb, “Picatinny” won’t fit Weaver, but Weaver will fit “Picatinny”.

FYI on that same note, Oly made some early flattop uppers with a Weaver rail. Some of them are still floating around. Not sure of the serial range. I got one and thought I had an out of spec upper but later found out it was a weaver rail. Oly swapped it out for me pretty cheap. Nice folks.

If I weren't such a clumsy, ill-fated, and incompetent boater, this might worry me. - ken_mays

Originally Posted By Slacker:I got one and thought I had an out of spec upper but later found out it was a weaver rail.

that fact that is was half and inch higher than every other flattop clued you in huh?

Moderation is for monks. RAHIt's a thankless job, luckily I have karma to burn.HEY YOU WASHINGTONIANS! http://ar15.com/forums/forum.html?b=8&f=15<font color=red>I am the signature virus, please put me in your signature so I can spread</fon

Nobody likes a smartass....Actually, the original clue was when I tried to slide an arms swan sleeve onto it (and onto a RIS).Seems they didn't line up very well....hmmmm...I did a little head scratching, then called Oly.

Originally Posted By Tweak:

Originally Posted By Slacker:I got one and thought I had an out of spec upper but later found out it was a weaver rail.

that fact that is was half and inch higher than every other flattop clued you in huh?

If I weren't such a clumsy, ill-fated, and incompetent boater, this might worry me. - ken_mays

The big issue being, what constitutes a “Picatinny Rail”, and probably as importantly what constitutes a “Picatinny Mount”.

Per that discussion, there are a lot of products floating around out there that are advertised as “Picatinny”, but in reality they are probably not meeting the true “Picatinny Spec”.

The issue on some rails is that the spacing between the recoil grooves is not consistent and back-to-back, and some have a channel or groove cut down the middle. In my (humble) opinion these rails are not “Picatinny Spec” and should not be marked or advertised as such. What do you guys think?

The issue on some mounts, is that the recoil tab does not run across the full length of the mount. In the case of the LaRue mounts, the recoil tab is only on the center of the mount. I am not real sure that this is an issue because I believe on a true “Picatinny Rail” the tab does not need to run across the full length, you will only have a problem if you are using one of the rails that has the channel or groove cut down the center and in my opinion is not to Picatinny Spec.

To be honest I have not been able to find anything on the “Mount Specs”, only the rail specs as outlined in MIL-STD-1913. As such I am not sure if there is a “Picatinny Mount Spec” that states that the recoil tab has to run across the full length of the mount. Can someone shed some light on the “Mount Specs”, if they do exist?

The big issue I have with this is that I purchase a lot of my items off of the internet, so I am relying on the word that it is to “Picatinny Spec”, which as it turns out is not always the case.

Oh well, I guess that is one of the reasons why Dremel Tools exist.

Thanks, Good Luck,“Capt Richardson”

"It takes a remarkable person not just to say a Creed and memorize a Creed, but to live by a Creed." S. Shughart

9-11-01 "All gave some, some gave all", rest in piece Brothers of FDNY